(1) Field of the Invention
The present invention pertains to a conveyor apparatus that conveys pluralities of objects arranged in two-dimensional arrays on the apparatus, and in particular to a holdback bar that selectively holds back the array of objects on the conveyor and releases the array of objects to be conveyed by the conveyor. More specifically, the present invention pertains to a holdback bar that is provided with a shock absorbing actuator that enables the holdback bar to move in the downstream direction of the conveyor when an array of conveyed objects contacts the holdback bar to cushion the impact of the array of objects with the holdback bar.
(2) Description of the Related Art
Many containers such as bottles, cans, boxes, etc., or other similar objects are packaged on pallets for transportation from a manufacturer to a user of the container or object. The pallet loads often include layers of the objects stacked one on top of another on the pallet. Each of the layers of the objects stacked on the pallet are typically separated from each other by a paperboard tier sheet that is positioned on top of each layer of objects stacked onto the pallet. The layers of objects and the tier sheets on which the layers rest are secured to the top surface of the pallet by banding, plastic sheet wrap or other equivalent methods. The pallet loads facilitate the transportation of a significant number of the objects on each pallet load from the manufacturer of the objects, through distribution and ultimately to the end user of the objects.
Various different types of conveyor apparatus are employed in arranging pluralities of objects into two-dimensional arrays of the objects that ultimately form the layers of the objects stacked on a pallet. Each two-dimensional array of the objects is conveyed by the conveyor apparatus from a portion of the conveyor system where the two-dimensional arrays are formed, to a palletizer that stacks each two-dimensional array of objects as a layer on the pallet. Typically, the layer of objects is stopped several times as it is conveyed by the conveyor system to the palletizer. For example, the layer of objects being conveyed by the conveyor apparatus would be stopped at some point along the conveyor apparatus so that a tier sheet can be positioned on top of the layer of objects.
The layer of objects is usually stopped by a holdback bar that moves into position over the conveying surface of the conveyor apparatus. The layer of objects comes into contact with the holdback bar and is held back by the bar as the conveyor continues to operate beneath the layer of objects. The conveying surface is not stopped so that other packaging procedures conducted along the conveyor can continue. When it is time for the layer of objects to continue along the conveyor path, the holdback bar is removed from its position over the conveyor and the previously held back layer of objects is released to be conveyed by the conveyor apparatus toward the palletizer.
In many conveyor systems in which objects are loaded as two-dimensional arrayed layers onto pallets, the faster the conveyor system can operate to load pallets the more cost efficient is its operation. One way of increasing the speed of the conveyor system is to increase the speed of the conveying surface of the system that conveys the layers of objects to the palletizer. However, the speed of the conveyor apparatus conveying surface cannot be increased to the extent that it will result in disarraying or throwing out of order the two-dimensional arrayed arrangement of the layers of objects conveyed by the conveying surface to the palletizer. For example, it has been observed that increasing the speed of the conveyor apparatus conveying surface increases the force of impact of a two-dimensional arrayed layer of objects with the holdback bar that stops and holds back the layer of objects on the conveying surface. The force of impact of the objects along the front row of the arrayed layer with the holdback bar is transmitted through the two dimensional arrayed arrangement of the objects to the objects in the last row of the array and often results in one or more of the objects in the last row bouncing back from the arrayed arrangement and falling over onto their side. This often causes down time of the conveyor system so that the objects of the arrayed layer that have fallen onto their side can be manually repositioned in the ordered two-dimensional arrayed arrangement before being conveyed further by the conveyor system to the palletizer. The down time of the conveyor system to reposition fallen objects into their two-dimensional arrayed layer arrangement defeats the purpose of operating the conveyor surface at an increased speed, i.e. increased cost efficiency of the conveyor system operation.
The conveyor apparatus of the present invention overcomes the shortcomings of the prior art conveyor apparatus described above by providing a cushioning holdback bar. The cushioning holdback bar cushions the impact of a two-dimensional arrayed layer of objects with the holdback bar in holding back the objects on the conveying surface and thereby prevents objects in the last row of the layer from falling over on their sides due to the impact of the layer with the holdback bar. As a result, the conveying surface of the conveyor apparatus can be operated at increased speeds without the drawback of the two-dimensional arrayed layer of objects impacting with the holdback bar causing several of the objects in the last row of the layer to fall over. Because the cushioning holdback bar of the invention enables the conveying surface of the conveyor apparatus to be operated at an increased speed, the cost efficiency of the conveyor apparatus is increased.
The conveyor cushioning holdback bar of the invention can be used in any portion of a conveyor system where it is desired to selectively hold back objects conveyed on the conveying surface of the system and release the objects to be further conveyed by the conveying surface of the system. The cushioning holdback bar can be used to holdback objects conveyed by the conveying surface in a single file line, or the cushioning holdback bar of the invention could be used to holdback two-dimensional arrayed arrangements of objects on the conveying surface. In the operative environment of the invention described herein, the cushioning holdback bar of the invention is employed with a conveyor apparatus that has a conveying surface that supports and conveys two-dimensional arrayed arrangements of objects.
The conveyor apparatus of the invention comprises a conveyor surface having a longitudinal length with opposite upstream and downstream ends. In the preferred embodiment the conveying surface is a moveable surface that supports and conveys pluralities of objects in a downstream direction from the upstream end of the conveying surface to the downstream end of the conveying surface.
The holdback bar of the invention is positioned over the conveying surface with the holdback bar extending laterally across the conveying surface. The holdback bar is moveable between lowered and raised positions of the bar relative to the conveying surface. In the lowered position of the holdback bar it is positioned to contact objects conveyed on the conveying surface and hold back those objects from moving further downstream as the conveying surface continues to move beneath the held back objects. When the holdback bar is elevated to its raised position over the conveying surface it releases the previously held back objects and allows them to be further conveyed in the downstream direction by the conveying surface.
An actuator is connected to the holdback bar. The actuator enables limited longitudinal movement of the holdback bar between first and second positions of the bar relative to the conveying surface. In the first position of the bar a two-dimensional arrayed arrangement of objects conveyed on the conveying surface are held back by the bar and are positioned at a desired position along the conveyor apparatus where a further process in the palletizing of the arrayed objects can be performed on the objects. In the illustrative example, the holdback bar in its first position holds the two-dimensional arrayed arrangement of objects on the conveying surface in a position where a tier sheet is deposited on top of the arrayed arrangement of objects. The second position of the holdback bar is spaced longitudinally in the downstream direction and vertically above the first position of the holdback bar.
In the preferred embodiment of the invention the actuator is a pneumatic cylinder and piston assembly. The cylinder and piston assembly is selectively supplied with air pressure to extend and retract a piston rod of the assembly relative to the cylinder and respectively move the holdback bar between its second and first positions.
A fluid pressure circuit communicates with the actuator. The circuit includes a plurality of valves, preferably solenoid operated valves, that selectively supply fluid pressure to the cylinder of the actuator to selectively extend and retract the piston rod of the actuator. Operation of the fluid circuit solenoid valves is controlled by a programmable logic computer. The computer controls the operation of the valves in response to signals it receives from a sensor positioned along the conveyor conveying surface adjacent the first position of the holdback bar.
In operation of the conveyor cushioning holdback bar of the invention, the holdback bar is held in its first position by the fluid circuit supplying the actuator with a low fluid pressure that retracts the piston and piston rod of the actuator in the actuator cylinder. As a layer of objects approaches the holdback bar on the conveying surface the layer will eventually reach the sensor positioned along the conveying surface. The sensor senses the presence of the arrayed layer of objects approaching the holdback bar and provides a signal to the programmable logic computer which in turn stops all fluid pressure being supplied to the actuator and exhausts the actuator cylinder. This causes the actuator cylinder to be in a neutral state with the piston and piston rod of the actuator being free floating in the cylinder. The programmable logic computer also generates a short adjustable time delay in response to receiving the signal from the sensor. The time delay is determined to coincide the downstream movement of the layer of objects on the conveying surface with controlling the fluid circuit to supply one side of the actuator with a low pressure that causes the piston and piston rod to move to their extended positions relative to the actuator cylinder. The movement of the piston and piston rod also causes the holdback bar to move from its first position towards its second position. The low pressure supplied to the actuator causes the holdback bar to move in the downstream direction from its first position toward its second position at a reduced rate of speed compared to the speed of movement of the layer of objects being conveyed by the conveying surface.
The difference in the rate of speed of the holdback bar and the rate of speed of the layer of objects will result in the layer of objects coming into contact with the holdback bar at a more gentle impact as compared to the layer of objects being stopped by a stationary holdback bar. As the arrayed layer of objects contacts the slower moving holdback bar, the arrayed layer of objects is restrained from moving at the higher speed of the conveying surface to move at the slower speed of the holdback bar creating a slowdown and cushioning effect of the holdback bar as it brings the layer of objects to a stop on the conveying surface. In this way, the actuator of the holdback bar functions as a shock absorber as it decelerates the layer of objects and brings the layer of objects conveyed on the conveying surface to a stop at an intermediate position of the holdback bar between the bar first and second positions.
The programmable logic computer then controls the fluid circuit to supply a low pressure to the opposite second side of the actuator cylinder while exhausting the air previously supplied to the one side of the actuator causing the piston and piston rod to move toward their retracted positions relative to the cylinder. This causes the holdback bar to move the two-dimensional arrayed layer of objects in an upstream direction, opposite the downstream direction, over the conveying surface. The two-dimensional arrayed layer of objects is gently forced to move upstream against the downstream motion of the conveying surface until the holdback bar reaches its first position. The further packaging procedures can then be performed on the arrayed layer of objects, for example a tier sheet can then be placed on the top of the arrayed layer of objects.
When the held back arrayed layer of objects and its tier sheet are ready for further downstream movement along the conveyor system, the programmable logic computer controls the fluid circuit to supply high pressure to the actuator cylinder that causes the piston and piston rod of the actuator to move quickly to their extended positions relative to the cylinder. The forward or downstream stroke of the piston and piston rod rapidly moves the holdback bar in the downstream direction separating the bar from the held back two-dimensional arrayed layer of objects. Simultaneously, the holdback bar is elevated to its raised position relative to the conveying surface. The downstream and upward movement of the holdback bar allows the two-dimensional arrayed layer of objects to clear the hold back bar as the layer of objects is conveyed by the conveying surface in the downstream direction. After the layer of objects conveyed by the conveying surface has cleared the area of the holdback bar as sensed by the sensor, the programmable logic computer then controls the fluid circuit to return the holdback bar to its first position relative to the conveying surface.
The conveyor cushioning holdback bar of the invention described above overcomes disadvantages associated with prior art holdback bars in that it cushions its impact with a two-dimensional arrayed layer of objects conveyed on a conveying surface. The cushioned impact of the bar with the two-dimensional arrayed layer of objects allows the conveying surface to be operated at an increased speed which increases the cost-efficiency of operation of the conveyor system.